Physical impacts or stress impulses commonly exist in daily life such as knocking and closing of doors and stepping on the ground. Stress impulse is characterized as an initial sharp peak followed by a quick attenuation. Although this impulse energy is ephemeral and small, it can still be harvested and re-used. An energy harvester (EH) is a device that converts ambient vibration energy, which would otherwise be wasted, into energy that can be used for a specific purpose. EHs using piezoelectric materials to convert ambient vibration into electrical energy may be used in a wide variety of applications with low power consumption.
For example, in U.S. Pat. No. 6,861,785, a self-powered remote control device having an EH is disclosed. This EH includes a striking means for generating a calibrated amount of mechanical energy for striking directly on a piezoelectric element with a predetermined force. This design, however, is limited to a specific type of striking force and cannot be used in conditions where physical impacts may not be pre-determined and can possibly damage the piezoelectric element when striking directly on it.
Another example of an energy harvester is described in U.S. Pat. No. 7,936,109, the disclosure of which is hereby incorporated by reference in its entirety. U.S. Pat. No. 7,936,109 describes an energy harvesting device that can harvest energy over a range of frequencies, including non-resonant frequencies. However, the energy harvesting devices disclosed in the '109 patent are typically used to harvest energy from continuous vibrations; thus, there is a need in the art for energy harvesting systems useful for converting a stress impulse caused by a physical impact to useful electrical energy.